1. Field of Invention
The present invention relates to hydrokinetic power-generating systems, methods, and devices that convert wave energy into electricity.
2. Description of Related Art
Ocean waves are a major, largely untapped energy resource. Research and development in this area is driven by the need to generate electricity from renewable energy resources, particularly in view of the rising level of CO2 in the earth's atmosphere from combustion of carbon fuels and the resulting impact on climate from global warming. A wave energy converter (WEC) captures energy from ocean surface waves, usually for electricity generation. However, prior attempts at wave power generation have not been widely accepted for various reasons.
Wave power is available in low-speed, high pulsating forces, and the motion of forces is not in a single direction. The force of wave action is concentrated in bursts of about 3 to 8 seconds and may repeat in random patterns both in wave period and size. Most commercial electric generators require a more steady flow of source energy. Furthermore any apparatus deployed on the ocean must be able to survive infrequent very large waves, raising the capital cost and maintenance.
The key to commercial viability of wave technology is a competitive levelized cost of energy (LCOE). Wave power is competitive when the total life cycle cost of power generation is low. The total cost includes the capital and maintenance costs, parts replacement and electric power delivery costs, and this in relation to the electric power generated, determines the “life-cycle” cost of energy. It is therefore desirable to provide a method and apparatus of obtaining optimum energy extraction from ocean waves at the least cost for the generating system. Moreover, a WEC must have minimal impact on the marine environment, such as fishing grounds and beach shoreline and must not interfere with ocean navigation.
U.S. Pat. No. 4,851,704 to Rubi, the entire disclosure of which is incorporated by reference herein, discloses a wave action electricity generation system that includes a floating platform that supports the system components on the water. Wave motion energy is converted into mechanical energy and an electricity generator converts the mechanical power transfer strokes into electrical energy. The converter includes a cylinder containing a lubricant, in opposed cylinder chamber portions, a first heavily weighted piston that is slidably and freely disposed within the body of the cylinder. The heavily weighted piston is slidably responsive to the wave motion energy of the body of water and is used to compress the fluid to produce respective compression power strokes in each of the cylinder chamber portions. The energy in the compression stroke is received by a second and third piston located in the cylinder chamber portions that further produce power transfer strokes through the ends of the cylinder. The power transfer strokes associated with the first and second pistons are further converted by a geared transmission to rotary motion that turns a flywheel coupled to an electricity generator. The electrical energy produced is then distributed to a remote power station via a power transmission line. This system relies on the rocking motion of the platform to convert the wave surface action, to movement of masses which are harnessed to drive an electric generator. This design captures the surface movement of waves and does not, per se, address the more substantial amount of energy available with a point absorber float, capturing the float displacement volume in a rising wave and the potential gravity forces on the wave as it recedes.
U.S. Pat. No. 5,889,336, the entire disclosure of which is incorporated by reference herein, to Tateishi discloses a power generating installation located in a shallow water area of the sea for generating power utilizing a shallow water wave. The system comprises a mooring located either in the sea or at the sea bottom, a chain having one end connected with the mooring and the other end to which a dead-weight is attached. A float is provided with a generator and a rotary member for rotating engaged with the chain. Rotary force of the rotary member produced when the float moves up and down according to an up-and-down motion of the wave is transmitted to the generator, thereby generating power. Substantial added float buoyancy is required to displace the mass of the dead weight and the chain connected thereto, along with the mass of the power conversion system within the float.
U.S. Pat. No. 7,453,165, the entire disclosure of which is incorporated by reference herein, to Hench discloses a method for harnessing power associated with ocean waves and converting that power into electricity. The apparatus is a buoy that houses a vertically oriented central shaft, a pendulum, and a generator. As the buoy tilts from the vertical under the influence of wave motion, the pendulum is accelerated and rotates about the central shaft. A centrally placed generator is mechanically driven by the rotating pendulum so that the pendulum's kinetic energy is converted into electricity. This design captures surface movement of waves and does not per se, address the more substantial amount of energy available with a point absorber float, capturing the float displacement volume in a rising wave and the potential gravity force as the wave recedes.
U.S. Pat. No. 7,808,120, the entire disclosure of which is incorporated by reference herein, to Smith discloses a wave energy generation apparatus utilizing a number of floats connected to a spar buoy via lever arms. The apparatus is anchored to the seabed at a desired location. In use, wave motion lifts and lowers the floats, thereby driving the lever arms to compress a hydraulic fluid, which is used to drive an electrical generator. This design is based on floats attached by lever arms to a central body. The hydrodynamic and buoyancy forces provided by wave action require structurally massive float lever arms, which in turn add to the buoyancy requirement of the system.
Yet, these prior art systems are not capable of producing cost-effective, utility-scale power output to meet modern energy needs. What is needed is a power-generating device for capturing power from ocean wave motion that provides a stable submerged platform and allows mechanically linked floats to have maximum exposure to wave action and concentrate the forces therefrom to the power converters. It is further desirable to provide a method of capturing the power of ocean waves that is efficient, cost effective to manufacture and maintain and is capable of withstanding severe weather events.